add content component.

components/app.tsx

@@ -1,7 +1,16 @@
 import * as React from "react";
+import {HeaderComponent} from "./header";
+import {SidebarComponent} from "./sidebar";
+import {ContentComponent} from "./content";
 
 export class AppComponent extends React.Component {
     render() {
-        return <div className="app-component">App</div>;
+        return (
+            <div className="app-component">
+                <HeaderComponent/>
+                <SidebarComponent/>
+                <ContentComponent/>
+            </div>
+        );
     }
 }

components/content.tsx

@@ -0,0 +1,7 @@
+import * as React from "react";
+
+export class ContentComponent extends React.Component {
+    render() {
+        return <div className="content-component">Content</div>;
+    }
+}